1. Field of the Invention
This invention relates generally to the providing of location-based services, including position information of a mobile station (MS) such as a cellular handset. More particularly, the invention relates to the distribution of location-based services over a network, particularly a network utilizing TCP/IP protocols such as the Internet and Web Services.
2. Related Art
Location-based services (LBS) or location-dependent services generally refer to the concept of providing wireless services that are dependent on a certain location, for example, the current position of a mobile station. The mobile station is typically a cellular handset but could also be a personal digital assistant (PDA) or some other type of mobile device, mobile station, or user terminal capable of interfacing with a network. A system providing LBS enables the user of a mobile station, or some other network component or entity (e.g., an application server), to make a request for the position of the mobile station or additionally for a service or application dependent on the position of the mobile station. The request may be a one-time request initiated by the user of the mobile station. For example, a mobile station may request a map showing its current location, driving directions from its current location to a desired destination, information regarding the existence and/or location of a certain type of business (e.g., restaurant, hospital, gas station, etc.) proximate to its current location, and the like. The request may also be triggered at predetermined intervals of time or in response to the occurrence of an event. For example, an application server may request the position of a mobile station in response to the mobile station passing from one geographical area to another area, for tracking or emergency purposes or to provide location-based information such as advertisements or coupons relating to proximate businesses. Hence, once the position of a mobile station is determined, location-based information may be provided to the requesting party. This information may be accessible from databases (which may be owned by content providers and made accessible to subscribers) and provided in a specific format in accordance with a specific application (e.g., maps, travel instructions, business-related content) and filtered in accordance with the position of the requesting party and as well as according to personal preferences set by or for the user and/or according to other predetermined rules. Generally, the position of a mobile station is obtained from a wireless network and/or a suitable positioning service such as a satellite positioning system, and particularly the Global Positioning System (GPS).
GPS (known as GPS NAVSTAR in the US) positioning technology is well-known to persons skilled in the art and thus need not be described in detail herein. Briefly, GPS is based on an existing constellation of twenty-four satellites and five monitoring stations situated around the planet enabling the satellites to broadcast spread-spectrum signals. These GPS signals may be utilized as references in determining the position of a mobile station. In addition to GPS, another positioning technology that may be utilized is the Russian system GLONASS (Global Navigation Satellite System), or the future European system currently known as the Galileo System, which operate in a similar fashion. In GPS, the satellites have 12-hour orbits and are positioned in six orbital planes with nominally four satellites in each plane, equally spaced at sixty degrees apart and inclined at fifty-five degrees relative to the equatorial plane. The satellites transmit carrier signals in two frequencies in the L-band, L1 (1.575.42 MHz) and L2 (1.227.60 MHz). Position is determined by operating a GPS receiver, which may be built into a cellular telephone or other mobile device, to acquire a sufficient number of satellites for pinpointing the location of the GPS receiver. Typically, a minimum of three satellites must be acquired so that their positions relative to the GPS receiver may be trilaterated. However, four satellites are preferred in order to obtain altitude information and ensure that the clock in the GPS receiver is synchronized with the more precise atomic clock in the satellites. Generally, the position of the GPS receiver is computed using the known position of the satellites in space (i.e., the orbits and times are known) and the known distances of the satellites from the GPS receiver (i.e., the travel times of radio signals from the satellites to the GPS receiver may be determined because their velocity at which radio signals propagate is known), and correcting or compensating for any delays and errors such as ephemeris errors. To enable measurement of the distance from a satellite to a GPS receiver, the satellite transmits a Pseudo Random Code (PRC) at precise intervals. The PRC is a stream of bits carrying the timing signal. The PRC also includes the satellite's address and thus each satellite has a unique PRC, enabling a GPS receiver to discriminate among the signals of different satellites. The PRC carried on the L1 carrier frequency, known as the Coarse Acquisition (C/A) code, is designated for civilian use.
Because a GPS receiver does not initially know its position, it must search for satellite signals in order to take the measurements needed to determine its position. From a cold start, the search can take approximately twelve minutes, which is considered much too long for the user of a mobile station. The time to acquire satellite data may be shortened by providing almanac data that essentially describe a long-term model of satellite trajectories, in addition to ephemeris, clock and satellite position data. Almanac data may be provided on a wireless network and updated regularly as new data is received from the satellites. Almanac data enables a GPS receiver to look for specific satellites by letting the GPS receiver know when they are likely to be overhead and visible to the GPS receiver, thereby reducing search time.
In order to improve the performance of GPS-based communications systems, advanced positioning methodologies have been developed. One such methodology is known as assisted-GPS or A-GPS technology, which generally refers to a system in which outside source such as an assistance server and reference network assist a GPS receiver in performing the tasks required for making range measurements, rendering position solutions, and the like. A-GPS promises to be a cost-efficient and time-efficient method for using a wireless network to distribute assistance or aiding data to GPS receivers, particularly GPS receivers integrated in mobile stations such as cellular handsets. Conventional implementations of A-GPS are well-known to persons skilled in the art and thus need not be described in detail herein. Briefly, in an A-GPS implementation, by utilizing the GPS receivers incorporated in a wireless network and estimating the location of a mobile station (e.g., the cell or sector in which the mobile station is located), the GPS signal that the mobile station will receive may be predicted and this information may be transmitted to the mobile station. The use of such assistance greatly reduces the size of the search space and shortens the time-to-first-fix (TTFF) down to a few seconds and potentially one second or less. Moreover, the A-GPS receiver in a mobile station may detect and demodulate signals that are an order of magnitude weaker than those required by conventional GPS receivers. In addition, while a mobile station could be equipped with a chip having all the functionalities of a full A-GPS receiver, only a partial A-GPS receiver is required in an A-GPS enabled mobile station. In the latter case, satellite data is downloaded over the mobile network, and the GPS receiver in the mobile station receives the data needed to calculate position every time the data are needed. In the typical architecture for an A-GPS system envisioned by industry, the system includes a mobile station whose position is sought and that is equipped with a partial GPS receiver, an A-GPS server equipped with a reference GPS receiver that can acquire the same satellites as the mobile station, and a wireless network infrastructure that includes cellular base stations and a mobile switching center. The A-GPS server obtains the estimated position of the mobile station (e.g., at the level of cell and sector) from the mobile switching center, monitors signals from GPS satellites seen by the mobile station, collects specific measurements from the mobile station, collects position results, and communicates the results to the mobile station.
The advantages provided by A-GPS and other advanced permutations of conventional GPS technology, such as improved accuracy, reduced positioning solution times and lower cost, make these advanced positioning technologies attractive for use in conjunction with location-based services. Ideally, a system capable of providing and distributing location-based services should be able to manage a large number of mobile stations over a large number of geographical areas without requiring the costly build-out of additional network infrastructure and without burdening existing infrastructure. In currently developing approaches for integrating GPS technology with wireless networks, a request for the position of a mobile station initiates the acquisition and refinement of GPS data as well as the generation any assistance or aiding data needed to compute the final position solution for the mobile station. In such a system, it can be appreciated that a large number of positioning requests by multiple users could have the potential for significantly overtaxing the networks involved and consequently defeating the advantages enabled by the positioning technology employed.
Therefore, there is a need for a distributed GPS processing system, and particularly one implementing location-based services, which overcomes the disadvantages set forth above and others previously experienced. In particular, there is a need for a system that distributes only one set of aiding data to all A-GPS users in the same location area without the need for a complex infrastructure for point-to-point and cell broadcasting position methods in as in current A-GPS technology.